Hydrogen peroxide monitoring

ABSTRACT

A method and apparatus for determining the hydrogen peroxide content of a fluid. The method includes: (a) contacting the fluid with a catalyst so as to permit decomposition of the hydrogen peroxide present in the fluid to oxygen and water; permitting the oxygen liberated to pass to gas meter; and (c) measuring the volume of oxygen liberated utilizing the gas meter, wherein the volume of oxygen liberated provides a measure of the hydrogen peroxide content of the fluid.

TECHNICAL FIELD OF THE INVENTION

The application is a national stage entry of PCT/GB00/03124, filing dateAug. 14, 2000.

The present invention is concerned with a method of monitoring thecontent of peroxide present in a fluid sample, and apparatus for such amethod.

BACKGROUND OF THE INVENTION

Hydrogen peroxide has been used as an oxidant in industrial applicationsfor many years. Hydrogen peroxide is, for example, a stronger oxidantthan chlorine or permanganate and has the advantage of non-pollutingdecomposition products.

Hydroxyl radicals (OH•) are highly oxidising species. The most commonlyaccepted mechanism for hydroxyl radical production is the photolysis ofhydrogen peroxide. Photochemical reduction of Fe³⁺ to Fe²⁺ (UV/Fentons)in the presence of hydrogen peroxide, increases the generation of OH•radicals and may yield a more effective system for oxidativedegradation.

A major application of peroxide is in advanced oxidation processesremoving recalcitrant organic contaminants, such as herbicides and PCB's(polychlorinated biphenyls). For example, the purification of watercontaining organic impurities by peroxide (approx 1%)/UV treatment hasbeen used since the early 1980's. In addition, peroxide together with UVand O₃, has been used at a field scale to treat ground watercontaminated with volatile organic compounds.

The partial oxidation of recalcitrant compounds may also beadvantageous. It has been shown by Carberry and Benzing (Water Sci. Tech23, 1991, 367-376) that two chlorinated aromatics showed enhancedbiodegradability after pre-oxidation with peroxide at molar ratiosbetween 2:1 and 6:1, with an optimum at 4:1.

The use of hydrogen peroxide as an oxidant has several advantages overother methods of chemical and photochemical water treatments, namely itsthermal stability, the ability to store on-site, its solubility inwater, and the lack of mass transfer problems of associated gases.

Peroxides are used in the removal of color, especially as a bleachingagent in the textile industry. In addition, peroxides are used in themanufacture of paper, and during waste paper recycling.

Other environmental applications include the oxidation of sulfides forodor control, corrosion control of waste pipes by addition of hydrogenperoxide to waste water, an additional oxygen source for overloadedactivated sludge plants and controlling filamentous bulking.

It can be seen from the above that the use of hydrogen peroxide inindustry has numerous advantages. However, the concentration of peroxideemployed in the industrial processes must be carefully controlled andmonitored for its efficient and cost effective usage.

There are many methods of monitoring hydrogen peroxide known in the art.Standard methods of monitoring hydrogen peroxide include titrimetric(typically based on the oxidation of hydrogen peroxide withpermanganate, followed by the reduction with acidic potassium iodide),gasometric, electrochemical calorimetric, chemiluminescent and acousticmethods. The results of these monitoring methods can then be used tocontrol the process.

The methods outlined above can be time consuming, sensitive tointerference, and have poor lifetime. They may not be so effective forprocess monitoring and control.

PCT patent specification WO98/30884 to BTG Källe Inventing AB (BTG)discloses a method and device for measuring the content of chemicals(such as hydrogen peroxide) used in connection with bleaching ofcellulose fibres. The method includes adding the enzyme catalase to thesample, which is agitated so as to permit the hydrogen peroxide todecompose and oxygen gas to be generated. The resultant oxygen gaspushes out a certain sample volume for the measurement of the sample;the sample volume is then, directly or indirectly, converted to a valuerepresenting the amount of hydrogen peroxide present.

In addition, the above mentioned patent specification suggests that itis not possible to measure directly the volume of oxygen produced.

SUMMARY OF THE INVENTION

These and other needs in the art are addressed by a method ofdetermining the hydrogen peroxide content of a fluid, which methodincludes;

(a) contacting the fluid with a catalyst so as to permit decompositionof the hydrogen peroxide present in the fluid to oxygen and water;

(b) permitting the oxygen liberated to pass to a gas meter; and

(c) measuring the volume of oxygen liberated utilizing the gas meter,

wherein the volume of oxygen liberated provides a measure of thehydrogen peroxide content of the fluid.

The term “fluid” is a term generally used in the art for any materialwhich can be pumped. Non-limiting examples of such fluids are solutions,slurries, pulps, gravel, etc.

It is preferred that the gas meter is arranged to measure low andirregular gas flows with a low back pressure. Typically, the gas meteris a low flow gas meter, such as the meter described in “On-line lowflow high precision gas metering systems”, Wat. Res, vol 29, page977-979 (1995), the disclosure of which is incorporated by reference.

The volume may be measured as an absolute volume, or as a rate ofevolution (in other words, the volume evolved in a unit time).

It is preferred that the volume of oxygen liberated in step (b) ismeasured directly.

It is preferred that the catalyst is an enzyme, such as catalase, whichmay be either soluble or immobilised. However other suitable catalystsmay be used. Preferably, the catalase is Hydrogen peroxide: hydrogenperoxide oxidoreductase, EC 1.11.1.6. The catalase catalyses thedecomposition of hydrogen peroxide to water and oxygen gas.

Typically, the amount of catalase present in step (a) is predetermined.It is also preferred that the catalase is present in an amount excessrelative to the hydrogen peroxide.

It is preferred that the mixing and catalysed release of oxygen in step(a) is carried out for sufficient time to decompose substantially all ofthe hydrogen peroxide present in the fluid.

The temperature of the process may be kept at a predeterminedtemperature, for example, in the range from 20° C. to 40° C.

Preferably, the oxygen liberated may be measured using a pressuretransducer or the like, such as a low-flow gas meter. Thus, the hydrogenperoxide content of the sample at any given time may be determined, forexample, in a continuous treatment process.

Preferably, the measurements by the gas meter of the oxygen liberatedfrom the sample are passed to a data acquisition system for processing,where, advantageously, the information may be calibrated to produce anaccurate reading of the hydrogen peroxide present in the sample.

Advantageously, when it is required to measure small amounts of hydrogenperoxide, such as about 25-500 mg.1⁻¹, the fluid sample is aerated priorto contacting with the catalyst.

The method according to the invention may be used in a wide range ofindustrial applications, for example, in paper processing, textileprocesses, steel industry and water treatment.

According to a second aspect of the present invention, there is providedapparatus for determining the hydrogen peroxide content of a fluid,which apparatus includes:

(a) a first receptacle arranged to (i) receive the fluid and a catalyst,and (ii) to permit decomposition of the hydrogen peroxide present tooxygen and water;

(b) a gas meter arranged to measure the oxygen evolved.

It is preferred that the flow of fluid and the catalyst are controlledusing at least one suitable peristaltic pump and/or at least onecentrifugal pump.

In a first embodiment of the second aspect of the present invention, theapparatus is suitable for use in continuous measurements. In thisembodiment, the fluid in the receptacle is maintained at a volume ofabout 15-60 cm³, preferably about 50 cm³. The volume may beadvantageously controlled using a manometer.

The apparatus preferably includes aeration means when it is required tomeasure small amounts of hydrogen peroxide, such as about 25-500 mg.1⁻¹.

In a second embodiment of the second aspect of the present invention,the apparatus is suitable for use in batch measurements. In thisembodiment, the fluid in the receptacle is maintained at about 25-2000cm³, preferably about 1000 cm³.

According to a third embodiment of the present invention, there isprovided a gas flow meter for use in the measurement of oxygen which isliberated as a result of the decomposition of hydrogen peroxide, thedecomposition being a result of contacting the hydrogen peroxide with acatalyst.

It is preferred that the gas meter comprises a three way solenoid valve,a sensitive differential pressure transducer and a ballast chamber.

The pressure transducer is preferably based on a steel diaphragm whichadvantageously is not significantly affected by temperature changes andis resistant to corrosion by water-saturated gases. Preferably, thesolenoid valve comprises a dry paddle solenoid valve, typically madefrom a material which is resistant to corrosive gases. Such a valve isadvantageously corrosion resistant.

The output from the differential pressure transducer may, in someembodiments, be smoothed, typically by an RC circuit or otherconventional methods.

It is therefore an aim of the present invention to provide a rapidmethod to monitor hydrogen peroxide over a wide range of concentrations.

It is a further aim of the present invention to provide a method foron-line monitoring of hydrogen peroxide which utilizes directmeasurement of the oxygen gas produced in the decomposition of hydrogenperoxide.

It is yet a further aim of the present invention to provide a monitorwhich is capable of monitoring hydrogen peroxide in “dirty” and “highsolid content” environments such as industrial process streams andeffluents without fouling or interference which is one of the majordrawbacks of currently available instruments.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 represents an embodiment of apparatus according to the presentinvention for measurement of hydrogen peroxide.

FIG. 2 is a graph of the oxygen produced from hydrogen peroxidestandards using a continuous operated hydrogen peroxide monitoringmethod.

FIG. 3 is a graph representing the correlation of oxygen producedagainst peroxide standards using a continuous operated hydrogen peroxidemonitoring method.

FIG. 4 is a graph of the oxygen produced from hydrogen peroxidestandards using a batch operated hydrogen peroxide monitoring method.

FIG. 5 is a graph representing the correlation of oxygen producedagainst hydrogen peroxide standards using a batch operated hydrogenperoxide monitoring method.

FIG. 6 shows oxygen evolution profiles for concentrations of hydrogenperoxide of 75, 100, 150, 200 and 300 ppm in water obtained by dosing of10% catalase using a batch operated peroxide monitoring method.

FIG. 7 shows the correlation of oxygen evolved against samples of knownperoxide concentration in water from 0-300 ppm obtained by dosing of 10%catalase using a batch operated peroxide monitoring method.

FIG. 8 shows the correlation of oxygen evolved against samples of knownperoxide concentration (0-300 ppm) prepared from paper pulp filtrates,pH adjusted to 10, obtained by dosing of 10% catalase using a batchoperated peroxide monitoring method.

FIG. 9 shows the correlation of oxygen evolved for samples of knownperoxide concentration in water (0-300 ppm) with dosing of differentconcentrations of catalase reagent into the chamber, 1,5 and 10%, usinga batch operated peroxide monitoring method.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be illustrated, by way of example only,with reference to FIG. 1 of the accompanying drawings, which representsan embodiment of apparatus according to the present invention formeasurement of hydrogen peroxide.

Standard hydrogen peroxide solutions were prepared from a 30% solution.The catalase, commercially available from Biocatalysts Limited, UK wasproduced from a selected strain of Aspergillus niger (this catalase isheat stable, active in a broad pH range and less susceptible to thedeactivating effects of hydrogen peroxide when compared with bovinesources). Various dilutions of the catalase supplied was used in theexperiments outlined below:

Continuous Experiments

Referring to FIG. 1, the continuous experiments were carried out in ahydrogen peroxide monitor 1 consisting of an acrylic reaction chamber 2(26 cm³ total volume), with a working liquid volume 3 of 17 cm³ (theworking liquid volume 3 is maintained at 17 cm³ by manometer 9); thecontents were mixed by a magnetic stirrer bar 4. The chamber was housedin a SI 60 D variable temperature controlled incubator (StuartScientific Co. UK) supplied by Fisher Scientific UK (not shown). Thechamber was connected to a LFM100 gas meter (G H Zeal Ltd).

The gas meter 5 comprises a solenoid valve 10, a ballast chamber 11, asensitive pressure transducer 12 and a control circuit and acquisitionsystem 13. Data from the monitor was logged on a PC with a interfacecard (DAQ 700) using LabVIEW (a trade mark of National Instruments,Newbury, UK). The Virtual instrument (VI) was configured to sample theoutput from the monitor at 1 minute intervals and download to “MicrosoftExcel” (both being trade marks) for off-line processing.

The standard hydrogen peroxide 14 was introduced into reaction chamber 2using a 505 μ peristaltic pump 6 (Watson-Marlow Ltd, Poole, UK) with an8-roller multi-channel pump head at a rate of 2.2 cm³ min⁻¹. Similarly,the 1% catalase solution 8 was introduced into reaction chamber 2 usinga 505 μ peristaltic pump 7 (Watson-Marlow Ltd, Poole, UK) with an8-roller multi-channel pump head at a rate of 0.075 cm³ min⁻¹. Duplicateruns of each hydrogen peroxide solution were performed at threedifferent temperatures of 30, 25 and 45° C. The oxygen production ratefor each run was calculated as the average of at least 25 minutes ofsteady state gas production. FIGS. 2 and 3 show examples of resultsobtained for measurements carried out in these experiments.

Experiments in Batch Mode

In one set of experiments the hydrogen peroxide monitor was similar inconstruction to that depicted in FIG. 1. It consisted of an acrylicreaction chamber having 70 cm³ total volume. The liquid temperature wascontrolled using a water jacket and a Grant FH15 (Cambridge, UK) flowheater. The chamber was connected to a LFM100 gas meter (G H Zeal Ltd,UK). Data from the monitor was logged on a PC with an interface card(DAQ 700) using LabVIEW (a trade mark of National Instruments, Newbury,UK). The Virtual instrument was configured to sample the output from themonitor at 1 minute intervals and download to “Microsoft Excel” (bothtrade marks) for off line processing.

A 25 cm³ sample of hydrogen peroxide was pipetted into the chamber,which was then sealed. A 1% solution of the catalase was then pumpedinto reaction chamber using a 505 μ peristaltic at a rate of 0.075 cm³min⁻¹ (Watson & Marlow Ltd., Poole, UK). The catalase was continuouslypumped into the reaction chamber until all the hydrogen peroxide hadcompletely degraded and gas evolution had ceased, the total oxygenproduction was than calculated taking into account the displacementcaused by introduction of catalase. Duplicate runs of each hydrogenperoxide solution were performed at 25° C. FIGS. 4 and 5 show examplesof results of experiments carried out with this monitor measuring from0.25 to 1.5% hydrogen peroxide solutions in sodium dihydrogenorthophosphate buffer at pH7.

In a further set of experiments, the hydrogen peroxide monitor consistedof an acrylic chamber with a working volume of 1 litre. The reactionchamber was located in a temperature controlled enclosure to maintainthe temperature of the reaction. The contents of the reaction chamberwere mixed by recirculation of the reactor contents by means of acentrifugal pump. The reaction chamber was connected to a low flow gasmeter, the technology as described previously. A data logger recordedoutput from the gas flow meter at predefined intervals and this wasdownloaded via an RS232 port using “Easy Log” software onto a PC wherethe data was processed off-line using “Microsoft Excel”, both beingtrade marks.

For measurement, the chamber was filled with pre-aerated sample to thepredefined volume. The chamber was then sealed shut. A known volume ofcatalase reagent was then added. The gas flow due to injection of thereagent is known and compensated for. As catalyst was injected, acompensating volume was removed from the reaction chamber. The reactionwas allowed to continue until all oxygen evolved was measured. Theoxygen evolved passed to the gas flow meter where its passage throughthe meter was registered electronically in the data logger as a voltage.The hydrogen peroxide concentration could be calculated and wasproportional to the total measured evolved oxygen registered as acumulative voltage. The following equation can be used to determine thevolume of oxygen based on the voltage measurement.

1 mol O₂=25.41L (273.15 K,0° C.)

1 mol O₂=25.29L (308.15 K,37° C.)[p*V=n*R*T; V₁/V₂=T₁/T₂]

1 mol H₂O₂=0.5 mole O₂=12.645 L

1 mL O₂=0.1 V

C=reaction volume in litres

1mg/L* (34.01 mg/mmol)⁻¹*12.65 mL/mmol*0.1 V/mL*C=1ppm H₂O₂⇄y[ppmH₂O₂]=0.037 V/L*C  Equation:

The chamber was emptied before repeating the process. Duplicate runswere performed using hydrogen peroxide solutions with the reactionchamber incubated at 37° C. FIGS. 6 to 9 show examples of results ofvarious experiments carried out with this monitor for concentrations ofperoxide between 0-300 ppm in solutions of water, (FIGS. 6 and 7), paperpulp filtrates filtered through a 500 μm mesh adjusted to pH10 usingNaOH, (FIG. 8) and samples in water using different concentrations ofcatalase reagent, 1, 5 and 10%, (FIG. 9).

Results

The results of the experiments outlined above are given in theaccompanying figures, wherein:

FIG. 2 is a graph of the oxygen produced from hydrogen peroxidestandards using a continuous operated hydrogen peroxide monitoringmethod;

FIG. 3 is a graph representing the correlation of oxygen producedagainst peroxide standards using a continuous operated hydrogen peroxidemonitoring method;

FIG. 4 is a graph of the oxygen produced from hydrogen peroxidestandards using a batch operated hydrogen peroxide monitoring method;and

FIG. 5 is a graph representing the correlation of oxygen producedagainst hydrogen peroxide standards using a batch operated hydrogenperoxide monitoring method.

FIG. 6 shows oxygen evolution profiles for concentrations of hydrogenperoxide of 75, 100, 150, 200 and 300 ppm in water obtained by dosing of10% catalase using a batch operated peroxide monitoring method;

FIG. 7 shows the correlation of oxygen evolved against samples of knownperoxide concentration in water from 0-300 ppm obtained by dosing of 10%catalase using a batch operated peroxide monitoring method;

FIG. 8 shows the correlation of oxygen evolved against samples of knownperoxide concentration (0-300 ppm) prepared from paper pulp filtrates,pH adjusted to 10, obtained by dosing of 10% catalase using a batchoperated peroxide monitoring method;

FIG. 9 shows the correlation of oxygen evolved for samples of knownperoxide concentration in water (0-300 ppm) with dosing of differentconcentrations of catalase reagent into the chamber, 1, 5 and 10%, usinga batch operated peroxide monitoring method;

The method according to the invention may provide rapid measurement ofperoxide in sample sizes of 20 ml or above. The method is more rapidthan the existing titrimetric and colorimetric methods, and is notgenerally subject to interferences. The method can therefore also beused off-line to replace existing methods for peroxide determinationboth for industrial and research purposes.

We claim:
 1. A method of determining the hydrogen peroxide content of afluid, the method comprising: (a) aerating a sample of the fluid; (b)contacting the aerated sample with a catalyst so as to decompose thehydrogen peroxide present therein into oxygen and water; (c) passing theoxygen liberated in (b) through a gas meter; and (d) measuring thevolume of oxygen liberated in (b) utilizing the gas meter, wherein thevolume of oxygen liberated provides a measure of the hydrogen peroxidecontent of the fluid.
 2. The method according to claim 1, in which thegas meter is arranged to measure low and irregular gas flows with a lowback pressure.
 3. The method according to claim 1, in which the gasmeter is a low flow gas meter.
 4. The method according to claim 1, inwhich the volume of oxygen liberated in step (b) is measured directly.5. The method according to claim 1, in which the catalyst is an enzyme.6. The method according to claim 5, in which the enzyme is catalase. 7.The method according to claim 6, in which the catalase is hydrogenperoxide: hydrogen peroxide oxidoreductase, EC 1.11.1.6.
 8. The methodaccording to claim 1, in which the catalyst has at least one propertyselected from the group consisting of (1) soluble; and (2) immobilised.9. The method according to claim 1, in which (b) includes contacting theaerated sample with a predetermined amount of catalyst.
 10. The methodaccording to claim 1, in which (b) is carried out for a sufficient timeto decompose substantially all hydrogen peroxide present in the sample.11. The method according to claim 1, in which the sample is maintainedwithin a predetermined temperature range.
 12. The method according toclaim 11, in which the range is between about 20° C. and about 40° C.13. A method according to claim 1, further comprising: (e) generating aparameter value representing the volume of oxygen measured in step (d);and (f) passing the parameter value to a data acquisition system.
 14. Amethod of determining the hydrogen peroxide content of a fluid, themethod comprising: (a) contacting a sample of the fluid with an enzymecatalyst so as to decompose the hydrogen peroxide present therein intoto oxygen and water; (b) passing the oxygen liberated in (a) through agas meter; and (c) measuring the volume of oxygen liberated in (a)utilizing the gas meter.
 15. A system for determining the hydrogenperoxide content of a fluid, the system comprising: an aerator, theaerator disposed to aerate a sample of the fluid; a receptacle, thereceptacle disposed to receive a catalyst and an aerated sample of thefluid, the receptacle further disposed host catalyzation of the aeratedfluid sample by the catalyst wherein hydrogen peroxide within theaerated fluid sample decomposes into liberated oxygen and water; and agas meter, the gas meter disposed to measure the volume of liberatedoxygen.
 16. The system according to claim 15, further comprising: atleast one pump selected from the group, consisting of (a) a peristalticpump; and (b) a centrifugal pump.
 17. The system according to claim 15,further comprising: a manometer, the manometer disposed to maintain apredetermined volume of aerated fluid sample in the receptacle.